(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 20, 2020

(Date
of Event which Requires Filing of this Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e),240.13d-1(f) or 240.13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall
include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

*

The remainder of this cover page shall be filled out for a reporting persons initial filing on this form
with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be filed for the purpose of Section 18 of the Securities
Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 28226B 302

SCHEDULE 13D

Page 1 of 11

1.

NAME OF REPORTING PERSON

Nathan D. Hukill

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

United
States

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

IN

(1)

Disposed of pursuant to the Agreement and Plan of Merger (the Merger Agreement), dated as of
March 16, 2020, by and among the Issuer and Assertio Therapeutics, Inc., a Delaware corporation, Assertio Holdings, Inc., a Delaware corporation (Parent), Zebra Merger Sub, Inc., a Delaware corporation and wholly-owned subsidiary of
Parent and Alligator Merger Sub, Inc., a Delaware corporation, whereby each share of Issuer common stock was cancelled and converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing
price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent
common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 2 of 11

1.

NAME OF REPORTING PERSON

CR Group L.P.

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Delaware

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

IA

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 3 of 11

1.

NAME OF REPORTING PERSON

CRG Partners III L.P.

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Delaware

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

PN

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 4 of 11

1.

NAME OF REPORTING PERSON

CRG Partners III  Parallel Fund A L.P.

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Delaware

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

PN

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 5 of 11

1.

NAME OF REPORTING PERSON

CRG Partners III  Parallel Fund B (Cayman) L.P.

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Cayman
Islands

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

PN

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 6 of 11

1.

NAME OF REPORTING PERSON

CRG Partners III (Cayman) Lev AIV I L.P.

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Cayman
Islands

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

PN

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 7 of 11

1.

NAME OF REPORTING PERSON

CRG Partners III (Cayman) Unlev AIV I L.P.

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Cayman
Islands

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

PN

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 8 of 11

1.

NAME OF REPORTING PERSON

Loan Security Holdings I LLC

2.

CHECK THE APPROPRIATE BOX
IF A MEMBER OF A GROUP

(a) ☐ (b) ☐

3.

SEC USE ONLY

4.

SOURCE OF FUNDS

OO

5.

CHECK BOX IF DISCLOSURE OF
LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)

☐

6.

CITIZENSHIP OR PLACE OF
ORGANIZATION

Delaware

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

7.

SOLE VOTING POWER

None

8.

SHARED VOTING POWER

0(1)

9.

SOLE DISPOSITIVE POWER

None

10.

SHARED DISPOSITIVE POWER

0(1)

11.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

0(1)

12.

CHECK BOX IF THE AGGREGATE
AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13.

PERCENT OF CLASS
REPRESENTED BY AMOUNT IN ROW (11)

0%(1)

14.

TYPE OF REPORTING
PERSON

OO

(1)

Disposed of pursuant to the Merger Agreement, whereby each share of Issuer common stock was cancelled and
converted into the right to receive 2.5 shares of Parent common stock having a market value of $0.80 per share, the closing price on the day prior to the effective date of the merger, as provided in the Merger Agreement. As contemplated by the
Merger Agreement, the warrant to acquire shares of the Issuers common stock was replaced with a warrant to purchase Parent common stock at the same exchange ratio, and with an exercise price of $0.0004 per share.

CUSIP No. 28226B 302

SCHEDULE 13D

Page 9 of 11

This Amendment No. 3 to Schedule 13D (this Amendment) amends and supplements
the Schedule 13D previously filed on February 11, 2019 (the Initial Statement), as amended by Amendment No. 1 to the Initial Statement filed on July 3, 2019, and as further amended by Amendment No. 2 to
the Initial Statement filed on March 26, 2020 by the Reporting Persons (as defined below) relating to common stock, par value $0.01 per share (the Common Stock), of Zyla Life Sciences, a Delaware corporation (the
Company).

This Amendment is being filed as a result of the disposition of the Reporting Persons common stock and the warrant to
acquire common stock (the Iroko Warrant) pursuant to that certain Agreement and Plan of Merger (the Merger Agreement) by and among the Company, Assertio Therapeutics, Inc., a Delaware corporation
(Assertio), Assertio Holdings, Inc., a Delaware corporation (Parent), Zebra Merger Sub, Inc., a Delaware corporation and wholly-owned subsidiary of Parent (Merger Sub) and Alligator Merger Sub, Inc.,
a Delaware corporation. Unless otherwise indicated herein, capitalized terms used but not defined in this Amendment shall have the same meaning ascribed to such terms in the Initial Statement. Except as set forth herein, this Amendment does not
modify any information previously reported by the Reporting Persons in the Initial Statement.

The information contained on the cover pages of this Schedule 13D is incorporated by reference into this Item
5.

As a result of the consummation of the transactions contemplated by the Merger Agreement, none of the Reporting
Persons beneficially own any shares of common stock.

b)

Neither LSH, the CRG Entities, the CR Group nor Mr. Hukill have any power to vote or direct the vote of
(or any shared power to dispose or direct the disposition of) any shares.

c)

On May 20, 2020, the parties to the Merger Agreement consummated the transactions contemplated thereby.
Accordingly, the Reporting Persons disposed of the shares and the Iroko Warrant pursuant to the Merger Agreement, and accordingly received 11,467,185 shares of Parent common stock having a market value of $0.80 per share, the closing price on the
day prior to the effective date of the merger, as provided in the Merger Agreement, and a warrant to acquire an aggregate 6,091,148 shares of Parent common stock at an exercise price of $0.0004 per share.

d)

No person (other than the Reporting Persons) is known to have the right to receive or the power to direct the
receipt of dividends from, or the proceeds from the sale of, the shares or the Iroko Warrant.

Pursuant to Rule 13(d)-1(k)(1) promulgated under the Securities Exchange Act of 1934, as amended, each of the undersigned acknowledges and agrees that the foregoing statement on Schedule 13D is filed on behalf of the undersigned and
that all subsequent amendments to this statement on Schedule 13D shall be filed on behalf of the undersigned without the necessity of filing additional joint acquisition statements. Each of the undersigned acknowledges that it shall be responsible
for the timely filing of such amendments, and for the completeness and accuracy of the information concerning it contained therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to
the extent that it knows or has reason to believe that such information is inaccurate.